Biomedical subjects

R Necker

Publications and source records attributed to R Necker.

At least 37 records · Page 2Linked to original sources

PubMed1994

Projection of wing nerves to spinal cord and brain stem of the pigeon as studied by transganglionic transport of Fast Blue.

To see whether there is a topographic organization of forelimb nerves in the CNS of birds, the termination pattern of afferents from wing nerves of the pigeon in the cervical spinal cord and the brain stem was determined by the transganglionic transport of Fast Blue and HRP. Fast Blue turned out to be a very sensitive and nonselective tracer with a wider distribution of terminal labeling than with HRP. Thus, Fast Blue is a useful marker for complete mapping of the terminal fields of peripheral nerves. Despite considerable overlap of the terminal fields of individual nerves the areas of densest labeling were somatotopically organized in the spinal dorsal horn. This organization is very similar to that described for the mammalian forelimb. In the rostral cervical segments all nerves have a projection field in ventromedial parts of the dorsal horn but there is no topographic organization. In the medulla terminal fields appear in the dorsal column nuclei including the external cuneate nucleus and group x near the descending vestibular nucleus. In sharp contrast to mammalian species there is no topographic representation of individual wing nerves in these brain stem areas.

Amidines↗

PubMed1992

Spinal neurons projecting to anterior or posterior cerebellum in the pigeon.

Spinal afferent fibers have been shown to project both to lobules III-VI and lobule IX of the cerebellum in the pigeon. In the present investigation the cells of origin of these projections and the course of the axons at spinal levels have been studied by the retrograde transport of fluorescent dyes injected into both parts of the cerebellum. In the upper cervical segments labeled neurons are located predominantly in the ventral horn; the axons cross to the contralateral side. In the cervical enlargement labeled neurons concentrate in the avian cervical Clarke's column (ClC) and in cervical "spinal border cells" (SBC). The axons of ClC neurons project ipsilaterally into the dorsolateral funiculus and SBC project ipsilaterally into the ventrolateral funiculus. In caudal cervical and in thoracic segments dorsal horn neurons (laminae IV/V) are at the origin of an ipsilateral spinocerebellar pathway in the dorsalmost part of the lateral funiculus. In the lumbosacral enlargement there are mainly three spinocerebellar cell groups all of which project contralaterally into the ventral funiculus: ClC, SBC and paragriseal cells. During its ascent this pathway shifts to the lateral funiculus. In addition there is a crossed pathway from ventral horn cells throughout the spinal cord. Whereas approximately equal numbers of dorsal horn cells project to lobules III-VI and to lobule IX, the number of ClC neurons is strongly reduced after lobule IX injections and SBC neurons are nearly absent. Altogether lobule IX has a substantial input from dorsal horn neurons (cutaneous mechanoreception) whereas that to lobules III-VI is dominated by ClC and SBC (proprioreception).

Animals↗

PubMed1992

Electrophysiological mapping of body representation in the cortex of the blind mole rat.

The cortex of the blind mole rat (Spalax ehrenbergi) was explored for somatosensory responses with special reference to an extension into the occipital cortex which serves vision in sighted mammals. Head and body representation was similar as in other rodents or mammals. However, the somatosensory area extended far into the occipital cortex. No responses to auditory or visual stimulation were found caudal to the somatosensory area. However, auditory responses were recorded in an area lateral to and slightly caudal to the head representation. It is concluded that in this naturally blind animal the area normally occupied by the visual cortex serves somatosensory function.

Animals↗

PubMed1991

Cells of origin of avian postsynaptic dorsal column pathways.

Whereas in the cervical spinal cord of pigeons lamina IV and medial lamina V neurons are at the origin of postsynaptic pathways to the dorsal column nuclei, lumbar lamina IV neurons do not project substantially beyond the cervical enlargement. There is, however a distinct group of medially located lumbar lamina V neurons which projects ipsilaterally to the dorsal column nuclei.

Animals↗

PubMed1991

A novel spinal pathway and other connections to the spinocerebellum in the pigeon.

Avian dorsal column nuclei do not project to the cerebellum. Injections of fluorescent tracers into the spinocerebellum of homing pigeons (Columba livia) disclosed a group of neurons located rostral to the dorsal column nuclei which receives spinal primary afferents, as confirmed by double-labeling experiments. Since this group has some similarities to the mammalian group x (location medial to the restiform body, spinal afferents, efferents to the cerebellum), this name was adopted for the pigeon. Further brainstem nuclei projecting to anterior or posterior spinocerebellum and with some relevance to transmission of spinal signals are described.

Afferent Pathways↗

PubMed1990

Cells of origin of ascending and descending as well as branching fibers in the cervical spinal cord of the pigeon.

Ascending and descending projections of spinal neurons (cervical enlargement) were studied with the retrograde transport of horseradish peroxidase (HRP) and with the fluorescent tracers Fast blue and rhodamine isothiocyanate (single and double labeling). Ascending and descending projections arise from the same laminae of the spinal grey except for neurons in contralateral lamina I and avian cervical Clarke's column which have ascending fibers only. A significant number of cervical nucleus proprius neurons (lamina IV) descends to the lumbar enlargement. Neurons with branching fibers were rare (less than 10 per cent).

Afferent Pathways↗

PubMed1990

Sensory representation of the wing in the spinal dorsal horn of the pigeon.

Somatotopic organization and response characteristics were examined in 234 dorsal horn neurons in the cervical enlargement of the spinal cord of anesthetized pigeons. Neurons located in the nucleus proprius (laminae III-V) were activated by light mechanical stimulation (movement of feathers) of cutaneous receptors. Both slowly adapting and rapidly adapting responses were observed, the latter being more numerous. Although most neurons responded to vibratory stimuli, an input from Pacinian-like receptors (Herbst corpuscles in birds) has still to be demonstrated. There was no evidence of an input from high-threshold receptors (nociceptors). Latencies to electrical stimulation of the receptive field suggest a contribution of large myelinated afferent fibers only. Neurons in the avian Clarke's column (within lamina V of the cervical enlargement) were activated by proprioreceptor stimulation. Receptive fields were usually small but larger on proximal parts of the wing (forearm and arm) than on distal parts (hand with fingers). There was a distinct topographic organization of receptive fields. Rostral parts of the wing (prepatagium, alula) were represented rostrally (C12, C13) and caudal parts (secondaries) caudally (C14). Furthermore, distal and ventral parts of the wing were represented medially and proximal and dorsal parts laterally. Despite its very specialized function (bird flight) the somatotopic representation of the wing in the spinal dorsal horn is very similar to that of the forelimb of mammalian species.

Animals↗

PubMed1989

Analysis of avian cold receptor function.

The response characteristics of facial specific cold receptors of the pigeon were studied quantitatively by recording single unit activity from the trigeminal ganglion at various stimulus conditions and subsequent analysis of the discharge pattern. Responses to maintained temperatures as well as to cooling steps were qualitatively identical to those seen in the corresponding mammalian cold receptor populations, but avian cold receptors were generally less sensitive, particularly to dynamic stimuli. The major differences between avian and mammalian cold receptors were that avian cold units only occasionally discharged in periodic groups of impulses at constant temperatures and that there was no indication of cyclic receptor events being involved in the dynamic response to cooling, as it is the case in all mammalian cold sensors. Additionally, the temporal pattern of the grouped discharges was less regular in avian cold units. Application of calcium, EGTA and menthol revealed a comparatively low dependence of cold receptor function on external calcium. The results provide evidence that calcium-controlled processes and periodic receptor events contribute only insignificantly to the signal transduction of avian cold receptors. This indicates a different functional organization of the transducer processes of avian and mammalian cold receptors.

Action Potentials↗

PubMed1989

Spinothalamic projections in the pigeon.

The spinothalamic projection in an avian species, the pigeon, was studied both with anterograde and retrograde means. Anterograde transport of wheatgerm agglutinin conjugated horseradish peroxidase (WGA-HRP) was used in order to determine the termination of the spinothalamic tract in the thalamus. Application to the lumbar enlargement of the spinal cord resulted in a dense terminal field in a thalamic nucleus now known as n. dorsointermedius ventralis anterior (DIVA). Less dense labeling was found in the thalamic nuclei n. intercalatus thalami (ICT), n. subrotundus (SRt) and possibly stratum cellulare externum and internum (SCE/SCI). After application of WGA-HRP to the cervical enlargement there was no labeling in the above-mentioned nuclei and only one distinctly labeled terminal in n. dorsolateralis posterior (DLP). Under electrophysiological control the fluorescent tracer Fast blue was applied to the DIVA. A considerable number of retrogradely labeled neurons was found in the lumbar enlargement only (contralateral intermediate grey). These results show that there is a substantial direct spinothalamic projection from the hindlimbs (legs) but not from the forelimbs (wings) in pigeons.

Amidines↗

PubMed1989

Effects of hypothalamic lesions on temperature regulation in pigeons.

The effect of hypothalamic lesions on temperature regulation was studied in pigeons by recording deep and skin temperatures, shivering, panting and oxygen consumption. Thresholds of shivering and panting were assessed before and after lesions. Survival was 100% when lesions were done in awake animals in a cool environment. Lesions anterior to the anterior commissure which included the preoptic area resulted in an increased threshold of panting or a lack of panting response at body temperatures up to 44.5 degrees C. Shivering response was unchanged in these animals. Lesions posterior to the anterior commissure were followed by a lack of shivering response with no change in panting threshold. This points to a segregation of the hypothalamic structures controlling heat loss and heat gain in the pigeon.

Animals↗

PubMed1989

Cells of origin of spinothalamic, spinotectal, spinoreticular and spinocerebellar pathways in the pigeon as studied by the retrograde transport of horseradish peroxidase.

The cells of origin of spinal neurons projecting to the thalamus, the midbrain, the reticular formation, and the cerebellum in the pigeon were studied with the method of retrograde transport of horseradish peroxidase (HRP). Only few spinal cells project up to the thalamus and to the tectum and their location is at the base of the dorsal horn (lamina V) and in the intermediate or ventral spinal grey matter (most contralateral). However, many cells in the dorsal column nuclei (including external cuneate nucleus) project up to these brain areas. Many spinal neurons project to the caudal brainstem and reticular formation. With medioventral injections of HRP labeled cells were found in lateral lamina I (bilateral) and laminae V-VIII (most contralateral) with a concentration in lateral lamina V/VI and lamina VIII. With dorsolateral brainstem injections there was a predominance of lamina I neurons, located bilaterally at the dorsolateral corner of the dorsal horn near Lissauer's tract. These results show that spinal cells, which in mammalian species project up to the thalamus, predominantly end in the caudal brainstem. Injections into the cerebellum disclosed that not only cells of Clarke's column but also sofar not known "spinal border cells", located dorsal to and in part intermingled with the motoneurons, are cells of origin of spinocerebellar tracts and that both groups of cells occur at the cervical and at the lumbar enlargement.

Animals↗

PubMed1987

Thermoregulatory responses of febrile sheep to spinal and hypothalamic heating.

Fever was induced by the intravenous injection of 0.25 microgram/kg of lipopolysaccharide (LPS) from Escherichia coli in eight conscious sheep exposed to ambient temperatures adjusted to the lower range of thermoneutrality. Chronic spinal or hypothalamic thermodes were perfused with water of 44 degrees C for 20 min or for most of the rising phase of fever (100 min of the mean 166 min total rise time). The effects of spinal and hypothalamic heating were identical. Thus, before LPS, spinal or hypothalamic heating did not affect the rate of O2 consumption (VO2) but increased skin blood flow (as indicated by skin temperatures) and elicited panting; therefore rectal temperature (Tre) fell. During fever rise, the already reduced skin blood flow and respiratory rate were not affected by spinal or hypothalamic heating, but the increased VO2 was reduced; consequently, the rise in Tre was attenuated. During the plateau phase of fever, all responses were similar to those seen before LPS. In febrilysis, heating strongly enhanced the operating heat loss mechanisms and, hence, augmented the fall in Tre. Thus, although the thermoeffectors activated by spinal or hypothalamic heating were modified during the different stages of fever, the effect on body temperature was nearly the same. Therefore there seems to be no change in spinal or hypothalamic thermosensitivity during fever in sheep.

Animals↗

PubMed1986

Cells of origin of ascending pathways in the spinal cord of the pigeon.

Horseradish peroxidase was applied to ascending spinal pathways at high cervical levels to determine the cells of origin of these pathways in the pigeon. In addition to primary afferent fibers many ipsilaterally located lamina IV neurons of cervical segments project to the dorsal columns, indicating a substantial postsynaptic dorsal column pathway in birds. Cells projecting in the dorsolateral part of the white matter were predominantly located in lamina I and V throughout the spinal cord (bilaterally) and in the avian Clarke's column (ipsilateral at cervical and contralateral at lumbar levels). Neurons in the ventral horn (laminae VI-VIII) project to lateral and ventral parts of the lateral funiculus.

Afferent Pathways↗

PubMed1985

Central projections of the radial nerve and of one of its cutaneous branches in the pigeon.

After horseradish peroxidase (HRP) treatment of the radial nerve and of a cutaneous branch of this nerve, dense labeling of afferent terminal fields was found in laminae I-III of the dorsal horn of the spinal segments C11 and C12. However, treatment of the cutaneous branch labeled only lateral parts of the dorsal horn. This points to a distinct somatotopy. Labeling was also observed in the dorsal column nuclei and a rostral terminal field near or within the pars interpolaris of the descending trigeminal system. No labeling was observed after dorsal rhizotomy.

Animals↗

PubMed1985

Projection of a cutaneous nerve to the spinal cord of the pigeon. I. Evoked field potentials.

Evoked field potentials have been recorded from the spinal cord after electrical stimulation of a cutaneous nerve in the pigeon. Four different postsynaptic negative waves (N1 to N4) could be discerned. These waves were obviously due to monosynaptic activation via the four different afferent fiber groups described for this cutaneous nerve (Necker and Meinecke 1984). Precise localization showed that large fibers project to deeper, medially located areas of the dorsal horn (near lamina IV) whereas smaller fibers project primarily to more laterally located superficial layers. A laterally recorded N-wave which was due to the activation of large fibers had a latency which indicated a disynaptic pathway.

Afferent Pathways↗

PubMed1985

Projection of a cutaneous nerve to the spinal cord of the pigeon. II. Responses of dorsal horn neurons.

The responses of dorsal horn neurons to both electrical stimulation of a cutaneous nerve and natural stimulation of skin receptors have been studied in an avian species, the pigeon. Neurons located in either lamina I or lamina IV were recorded. Most lamina IV neurons had short-latency responses to electrical stimulation of a cutaneous nerve and were activated by stimulation of sensitive mechanoreceptors. This points to an input from mechanoreceptors innervated by large afferent fibers. Lamina I neurons which were usually located near the entrance zone of small fibers had longer latency responses and had often an input from several groups of afferent fibers including C-fibers. Many lamina I neurons were activated specifically by noxious stimulation. Some had an input from sensitive mechanoreceptors but possibly through an additional synapse. A few lamina I neurons responded specifically to activation of cold receptors. Some dorsal horn neurons showed segmental inhibition. Altogether, the characteristics of dorsal horn neurons in the pigeon studied so far were similar to those in mammalian species.

Afferent Pathways↗

PubMed1979

Methods of analyzing dynamic responses of temperature-sensitive neurones.

Methods are described for analyzing the dynamic responses of temperature-sensitive neurones or receptors using a computer facility. The methods allow correlation of impulse frequency with temperature changes or with the rate of temperature changes independent of the time course of the temperature change. Different types of dynamics responses and different thermal sensitivities could be distinguished.

Animals↗

PubMed1979

Cyclic and non-cyclic variations of spinal cord temperature related with temperature regulation in pigeons.

1. The temperature of the spinal cord (Tvc) was measured in unanaesthetized pigeons at different ambient temperatures (Ta). 2. In short-term experiments spontaneous or noncyclic variations of Tvc at constant (20 and 10 degrees C) and changing Ta were correlated with the amplitude of the electromyogram EMG) which indicates shivering, i.e., heat production. At constant Ta no unequivocal correlation between Tvc (and also Tskin) and EMG was found. During ambient cooling there was often an increase of Tvc which resulted in a positive correlation whereas there was a negative correlation to Tskin. 3. In long-term experiments (24h, LD 12:12Y cyclic variations of Tvc were measured at different Ta and ocrrelated with O2-consumption, i.e., heat production. As with body temperature Tvc was lowered during the dark phase of the diurnal cycle. In the light phase both Tvc and heat production increased with decreasing Ta which results in a positive correlation. In the dark phase there was a smaller increase in heat production but a decrease in Tvc, i.e., a negative correlation. 4. The results show that natural variations of Tvc are often positively ocrrelated with heat production. This is in contrast to experimental changes of Tvc where a clear negative correlation to heat production can be observed.

Animals↗